1. Field of the Invention
The present invention relates to a telescoping boom apparatus and particularly to an extension and retraction system for such apparatus.
2. Description of the Prior Art
Multiple section, telescoping boom apparatus is well known in the prior art for extension and retraction of a working platform or basket which is suspended from the outermost section. A typical application for such an apparatus is the harvesting of fruit from tall trees such as date trees. The boom apparatus is normally attached to a mobile platform, and pneumatic or hydraulic cylinders are provided to pivot the boom sections about a horizontal axis for raising and lowering the picker's basket.
The height of such date palms makes use of a four section boom apparatus preferable, one section being an inextensible base section which is pivoted to the mobile platform. The other boom sections are longitudinally extensible by operation of a pneumatic or hydraulic cylinder in conjunction with a cable and sheave arrangement.
Some systems of the prior art employ a single cylinder connected between the base section and the outermost section, but such an arrangement is generally impractical where the length of the extended sections is great. Other prior art systems employ a plurality of cylinders, one for each section, but these are unduly complex and involve high production and maintenance expense. A system which is preferred employs a single cylinder to extend one of the sections, with a cable and sheave arrangement being arranged to automatically extend the other sections in response to extension of the first section. However, this arrangement is not entirely satisfactory. For long boom extensions the piston rod of the cylinder is necessarily of relatively large diameter, very expensive, and subject to deflection at maximum boom extensions. Further, although the cable and sheave arrangement is generally satisfactory to extend the boom sections, there is no means for positively retracting the sections. Instead, the practice has been to pivot the boom sections upwardly at an angle such that their weight telescopably retracts them. It is desirable to have some means for retracting the boom sections at lesser angles of elevation.